Generally, traveling environments of a vehicle, especially visibility, change with weather conditions. Therefore, a navigation system or the like mounted on a vehicle acquires, from the outside, information about weather conditions, and presents the acquired information.
In recent years, a system for observing weather based on information acquired from vehicles has been developed. As a system of this type, a system (weather information processor) for observing weather based on a weather condition variable measured by a weather information sensor mounted on a first vehicle is known, as disclosed in Patent Document 1, for example. This system includes, as a weather information sensor, a raindrop sensor, a barometer, a sunshine sensor, a thermometer, and hygrometer. In this system, the amount of rainfall, the illuminance of the sun on the vehicle, the respective temperature and humidity levels inside and outside the vehicle, and the like are measured, as weather condition variables, by the raindrop sensor, the barometer, the sunshine sensor, the thermometer, the hygrometer, and the like. Next, it is determined whether the amount of deviation between this measured weather condition variable and the previous weather condition variable is equal to or higher than a predetermined value. When it is determined that the amount of deviation is equal to or higher than a predetermined value, weather change detection information is generated, which indicates the amount of deviation and a weather change position indicating the current position of the first vehicle, where the weather condition variable has been measured. Then, the weather change detection information thus generated is transmitted to a second vehicle different from the first vehicle, and is presented to, for example, the driver through an apparatus mounted on this second vehicle.